I bought the Zalman ZM-F2 92 mm fan that can be run in full mode and silent mode. I'm running it in silent mode on the SLK900a right now and it's very silent. Unless the rest of your components in your case are dead silent, you won't hear it. I'd say it's on par with the Panaflo L1a in the 80 mm as far as noise.
I don't like the Stealth fans. I think they fudge their numbers. I compared a 80 mm Stealth fan to other quiet 80 mm fans a while back and it was clearly louder than the rest even though it was rated at the same db. Also, I think that their packaging is expensive and wasteful. I'd rather have Vantec drop the price on the fan a few bucks than put it in such a fancy box.
Sal